This invention relates to a valve for controlling fluid flow and, more particularly, to a piezoelectric valve which is neither solenoid or servo assisted. In this specification and claims, reference to fluid(s) includes both liquid(s) and gas(es).
A number of piezoelectric valves have been proposed embodying a valve element in the form of either a circular disc or a beam. The circular disc or beam element is usually a laminated structure having a piezoelectric ceramic wafer bonded to one or both major surfaces of a substrate having a different coefficient of expansion from the wafers. Alternatively, the valve element may comprise two oppositely polarised piezoelectric ceramic wafers of differing coefficients of expansion and bonded to each other in face to face relationship. Application of an electric field to the wafers causes the so constructed element to deflect in the same way as a bimetallic strip.
U.S. Pat. No. 4,545,561 describes and claims a piezoelectric valve for controlling fluid flow. The valve includes a split or two part housing between which parts a shallow and generally cylindrical cavity is formed. The split housing is divided along a parting plane which is parallel to opposite circular end planes of the cylindrical cavity. One part of the housing includes inlet and outlet fluid apertures for incoming and outgoing fluid whereas the other part of the housing contains first and second flexible electric contacts elements connectable to opposite terminals of a voltage source. A deformable conductive plate element is captured at its perimeter between the two parts of the split housing and has a piezoelectric wafer bonded on that side thereof opposite from the fluid apertures and in a position proximate to the center of the plate element such that the piezoelectric wafer is supported by the plate element without contacting the housing at its perimeter.
When assembled, the first flexible electric contact element is pressed into electrical contact with the piezoelectric wafer and the second flexible electric contact element is pressed against the deformable conductive plate element so that, upon actuation of the piezoelectric element by the voltage source, the plate element is caused to travel between a first position in which the plate element occludes the passage of fluid between at least one of the fluid apertures and the cavity and a second position in which the plate element is deformed away from at least one fluid aperture allowing fluid flow through the cavity between the inlet and outlet apertures.
It will, therefore, be appreciated that the valve described in U.S. Pat. No. 4,545,561 is an example of a circular disc type piezoelectric valve in which the disc is captured at its perimeter. On the other hand, a beam element, sometimes referred to as a bender element, type piezoelectric valve is described and claimed in PCT Application WO86/07429. The valve according to WO86/07429 comprises a housing defining a cavity, an inlet conduit means having one end terminating as an inlet orifice, said inlet orifice having a cross sectional area and being at a predetermined location and within said cavity and having another end of said inlet conduit means in fluid communication with a fluid supply;
an outlet conduit means having one end terminating as an outlet orifice at a predetermined location within said cavity and said outlet orifice having a predetermined cross sectional area, another end of said outlet conduit means in fluid communication with a means for using fluid from said fluid supply and having an effective fluid storage volume.
a bender element appropriately positioned within said cavity and affixed to said housing means, having a means adapted for providing signal communication between said bender element and a controllable flow control signal, said signal effective to cause said bender element to deflect a controlled amount thereby permitting an amount of said fluid to flow at a controlled flow rate through said valve device; and
a first sealing means affixed to said bender element to effectively seal, during the absence of said flow control signal, said outlet orifice.
U.S. Pat. No. 3,360,664 describes an electromechanical transducer as opposed to a valve. The transducer includes a pair of spaced active components in the form of juxtaposed piezoelectric ceramic discs mounted to undergo flexure using a special hinge component when subject to acoustic energy. The active components may be in the form of perimetrally fixed discs or beams supported at their ends. FIG. 9 of U.S. Pat. No. 3,360,664 discloses a transducer in which an active vibrating piezoelectric element in the form of a disc is centrally fixed to a post (a node during flexure) whereas the ends of perimetral portions of the disc element form during flexural vibration anti-nodes. Upon excitation of the piezoelectric element, the degree of vibration of the anti-nodes is transmitted via connecting rods to a plate which is thereby displaced. Conversely, displacement of the plate by acoustic energy applied to the plate bands the piezoelectric element radially in a flexural node. Thus, the transducer disclosed in U.S. Pat. No. 3,360,644 is a device capable of transmitting and receiving wave energy under the agency of a piezoelectric element during flexure.